The ports, airports and coastal infrastructures that have been in service for a long time are increasing, but financial resources and the number of engineers for facility maintenance are limited. As important port, airport, and coastal infrastructure functions should be maintained, the strategic maintenance, renewal, and other measures to maintain such functions are strongly required. Therefore, we are trying to establish methods for structure design and material selection which are excellent in terms of maintenance, and will develop techniques and technologies regarding various countermeasures for maintenance phase.

Research on infrastructure inspection and diagnosis techniques

Research on technologies for prolonging the life of infrastructure

As some parts of marine structures are difficult to inspect by eye, it is necessary to introduce monitoring using sensors and other devices in order to evaluate and predict the process of deterioration of their concrete and the efficacy of measures deployed to suppressdeterioration. In this study, we developed a technique that can evaluate and predict the performance of the structural components as a whole, integrating both numerical analysis and on-site monitoring. Specifically, we focused on the expansion-induced deterioration resulting from the alkali silica reaction (ASR) and were able to successfully simulate the aforementioned deterioration process facilitated by ASR through finite-element analysis. We then developed an analytical platform that can examine the structures of components while factoring in their deterioration conditions and started on-site monitoring of actual marine structures using the platform.

Concerning ROVs for inspecting the superstructures of piers, we integrated into them our technology that would allow them to deal with external disturbances and improved the countersteering capability that was included in the stationary positioning system (i.e., thrust adjustment, countersteering, etc.) implemented in the previous year. We then took the pier superstructure inspection ROVs to three ports (one of which was during the night) and investigated the bottom surfaces of the pier superstructures there, which allowed us to verify the effectiveness of the ROVs and their upgraded stationary positioning capability in executing inspection tasks beneath piers where visibility is low. Furthermore, as the on-site tests investigated different types of piers such as inclined-pile and jacket-covered pier structures, the applicability of the techniques being developed to actual piers was verified.

We set up a long-term exposure test facility to examine a method of predicting concrete corrosion induced by chlorine, the cathodic protection characteristics that affect steel bars in reinforced concrete, the conentrated corrosion mechanism of steel components, and the cathodic protection characteristics present near LWL. We also acquired data on the durability of various wood materials in this study.

We have been continuously performing exposure tests (for 37 years as of FY 2021) at the Hazaki Oceanographical Research Station (HORS) to examine various coating methods for protecting steel piles in order to establish a method for predicting deterioration applicable to protective-coated steel structures. In addition, we worked on elucidating the deterioration mechanism of petrolatum-coated structures based on the findings from our accelerated weathering and indoor exposure tests along with the aforementioned exposure tests conducted at the HORS. We then summarized the results of the study conducted in the previous year (on the 18-year-old surface-coated pier superstructure) to verify the applicability of the anti-corrosion coating (surface coating method) to concrete port structures.

In order to solve the problem with pile head joints using precast concrete for installation at piers, we conducted a loading experiment and numerical analysis involving a 1/2-scale model comprised of steel-pipe piles and RC beams joined together. For this experiment, we used the commonly used method in road bridge construction for connecting the pile foundation and the footing to make the pile head joints. The experiment verified that the newly applied method was superior to the jointing method used in the previous year's experiment in terms of the structure it created, which allowed the pier model to sustain its load-bearing performance as the amount of displacement increased. However, as the model's load-withstanding mechanism involved the steel-pipe piles mainly handling the load on the compression side and the in-built rebars mainly handling the load on the tension side, we were able to determine that the decreased stationarity of the pile heads would not pose any issue in operational application.

Wire meshs are typically installed on the concrete pavements at airports to prevent the spread of cracks and maintain the integrity of the rebar joints underneath them, while preventing foreign objects from falling into the cracks. However, the effectiveness of this design and implementation method was not enough to be proven, so we conducted a study for this purpose. We used the test pavement that was constructed in the previous year and conducted a dump truck loading experiment on it, with and without wire mesh covering, to compare the results and determine whether the covering had any effect on the occurrence of cracks, but no significant difference was observed in the experiment.

To create a sustainable society, it is desirable to reduce the use of natural resources and CO2 emissions when constructing buildings (mainly made of concrete). It is also preferable to improve the performance and usable lifespans of structures, and enhance their safety margins against temporal deterioration and natural disasters. To this end, the use of recycled materials has proven to be effective (various slag frame materials, ground granulated blast-furnace slag, fly ash, etc.).However, these materials have not yet been widely used in actual construction projects. The non-use of these materials might be due to their undefined performance requirements, and the lack of a method for evaluating their longterm durability, etc.